At 00.53 hours on 23 May 1942, the unescorted and unarmed William Boyce Thompson (Master Hjalmus V. Rasmussen), en route in ballast from New York to Curaçao, was hit on the starboard side by one torpedo from U-558 while steaming on a nonevasive course at 10.5 knots about 120 miles south of Kingston, Jamaica in 16°26N/77°51W (grid EB 3855). The torpedo hit at #4 tank and opened a hole of 20 feet on the starboard and several small holes on the port side and the weather deck. While the #3 tank and the pump room flooded slowly, the tanker escaped northwards zigzagging at full speed in a smoke screen. The eight officers, 29 crewmen and two Navy signalmen on board reported no injuries. On 24 May, she arrived at Guantanamo Bay, Cuba and returned to service after being repaired.

At 06.07 hours on 7 July 1943, U-185 attacked convoy BT-18 about 175 miles east of Fortaleza, Brazil for a first time and reported two ships sunk and another damaged. In fact, the William Boyce Thompson and the James Robertson were sunk.

The William Boyce Thompson (Master Fred Charles Vosloh) was the ship of convoy commodore in station #41. The tanker was hit by one torpedo on the starboard side at the engine room, destroying the engine and the steering gear and killed one officer and three crewmen on watch below. As the ship began settling by the stern rapidly, twelve men panicked and abandoned ship in a lifeboat without orders. Three of them were later picked up by Jaguarão (CS 55) together with survivors from the other torpedoed ship, while the remaining men were picked up by USS Surprise (PG 63). Most of the eight officers, 32 crewmen, eleven armed guards (the ship was armed with one 4in and two .50cal guns), convoy commodore and five naval staff members abandoned ship after seven hours in two lifeboats and a raft and were also picked up by the corvette, which landed them at Recife on 10 July. One crewman later died of wounds ashore. The wreck of William Boyce Thompson remained afloat and had to be sunk by gunfire and depth charges from the escort vessels.

The master, Fred Charles Vosloh, had only 4 months earlier lost a ship to the same U-boat and commander when Virginia Sinclair was sunk by U-185 (Maus) on 10 March 1943.